Ecological Health in the Nation's Streams, 1993-2005

83 percent of assessed streams had at least one altered biological community

Assessments of stream health that are limited to a single biological community are likely to underestimate the effects of land and water use on stream health.

Annual high or low streamflows were modified in 86 percent of the assessed streams

Natural fluctuations of flows are critical to stream health because they build and maintain physical habitats, influence physical and chemical characteristics of water, and provide important life-stage cues for aquatic organisms.

Unraveling the effects of multiple factors on stream health

Stream health is often reduced due to multiple factors--temperature, nutrients, or pesticides. Understanding the interacting natural and manmade factors that influence aquatic communities is essential to implementing effective management strategies to protect stream health.